Silicon-containing electrodes and methods for preparing the same

This section provides background information related to the present disclosure which is not necessarily prior art.

Advanced energy storage devices and systems are in demand to satisfy energy and/or power requirements for a variety of products, including automotive products such as start-stop systems (e.g., 12 V start-stop systems), battery-assisted systems, hybrid electric vehicles (“HEVs”), and electric vehicles (“EVs”). Typical lithium-ion batteries include at least two electrodes and an electrolyte and/or separator. One of the two electrodes may serve as a positive electrode or cathode and the other electrode may serve as a negative electrode or anode. A separator filled with a liquid or solid electrolyte may be disposed between the negative and positive electrodes. The electrolyte is suitable for conducting lithium ions between the electrodes and, like the two electrodes, may be in solid and/or liquid form and/or a hybrid thereof. In instances of solid-state batteries, which include solid-state electrodes and a solid-state electrolyte (or solid-state separator), the solid-state electrolyte (or solid-state separator) may physically separate the electrodes so that a distinct separator is not required.

Many different materials may be used to create components for a lithium-ion battery. The negative electrode typically includes a lithium insertion material or an alloy host material. For example, typical electroactive materials for forming an anode include graphite and other forms of carbon, silicon and silicon oxide, tin, and tin alloys. Certain anode materials have particular advantages. While graphite having a theoretical specific capacity of 372 mAh·gis most widely used in lithium-ion batteries, anode materials with high specific capacity, for example high specific capacities ranging about 900 mAh·gto about 4,200 mAh·g, are of growing interest. For example, silicon has the highest known theoretical capacity for lithium (e.g., about 4,200 mAh·g), making it an appealing material for rechargeable lithium-ion batteries. Such materials, however, are often susceptible to huge volume expansion during lithiation and delithiation, which can lead to particle pulverization, loss of electrical contact, and unstable solid-electrolyte interface (SEI) formation, causing electrode collapse and capacity fading. Accordingly, it would be desirable to develop improved materials, and methods of making and using the same, that can address these challenges.

This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

The present disclosure relates to silicon-containing electrodes, to electrochemical cells including the same, and to methods of making and using the same.

In various aspects, the present disclosure provides an electrode for an electrochemical cell that cycles lithium ions. The electrode may include a silicon-containing electroactive material and a polyacrylate binder formed from a monomer selected from the group consisting of:

and combinations thereof.

In one aspect, the polyacrylate binder may have a molecular weight greater than or equal to about 250,000 g/mol to less than or equal to about 500,000 g/mol.

In one aspect, the electrode may include greater than or equal to about 0.5 wt. % to less than or equal to about 5 wt. % of the polyacrylate binder.

In one aspect, the electrode may further include greater than or equal to about 0.1 wt. % to less than or equal to about 5 wt. % of a conductive additive.

In one aspect, the electrode may further include greater than or equal to about 10 wt. % to less than or equal to about 50 wt. % of the silicon-containing electroactive material.

In one aspect, the electrode may further include a carbonaceous electroactive material.

In one aspect, the electrode may include greater than or equal to about 10 wt. % to less than or equal to about 50 wt. % of the silicon-containing electroactive material, and greater than or equal to about 40 wt. % to less than or equal to about 80 wt. % of the carbonaceous electroactive material.

In various aspects, the present disclosure provides an electrochemical cell that cycles lithium ions. The electrochemical cell may include a first electrode that includes a positive electroactive material, a second electrode that includes a negative electroactive material and a polyacrylate binder, and a separating layer disposed between the first and second electrodes. The polyacrylate binder may be selected from the group consisting of: poly(acrylic acid), poly(acrylic acid) fractional neutralized with magnesium, calcium, lithium, sodium, and/or potassium, poly(ethylene-co-acrylic acid), poly(ethylene-co-acrylic acid) fractional neutralized with magnesium, calcium, lithium, sodium, and/or potassium, poly(acrylamide-co-acrylic acid), poly(acrylamide-co-acrylic acid) fractional neutralized with magnesium, calcium, lithium, sodium, and/or potassium, poly styrene-block-poly (acrylic acid), polystyrene-block-poly(acrylic acid) fractional neutralized with magnesium, calcium, lithium, sodium, and/or potassium, poly(N-isopropylacrylamide-co-acrylic acid), poly(N-isopropylacrylamide-co-acrylic acid) fractional neutralized with magnesium, calcium, lithium, sodium, and/or potassium, and combinations thereof.

In one aspect, the polyacrylate binder may be a first polyacrylate binder and the first electrode may further include a second polyacrylate binder. The second polyacrylate binder may also be selected from the group consisting of: poly(acrylic acid), poly(acrylic acid) fractional neutralized with magnesium, calcium, lithium, sodium, and/or potassium, poly(ethylene-co-acrylic acid), poly(ethylene-co-acrylic acid) fractional neutralized with magnesium, calcium, lithium, sodium, and/or potassium, poly(acrylamide-co-acrylic acid), poly(acrylamide-co-acrylic acid) fractional neutralized with magnesium, calcium, lithium, sodium, and/or potassium, polystyrene-block-poly(acrylic acid), polystyrene-block-poly(acrylic acid) fractional neutralized with magnesium, calcium, lithium, sodium, and/or potassium, poly(N-isopropylacrylamide-co-acrylic acid), poly(N-isopropylacrylamide-co-acrylic acid) fractional neutralized with magnesium, calcium, lithium, sodium, and/or potassium, and combinations thereof.

In one aspect, the polyacrylate binder may have a molecular weight greater than or equal to about 200,000 g/mol to less than or equal to about 500,000 g/mol.

In one aspect, the second electrode may include greater than or equal to about 0.5 wt. % to less than or equal to about 5 wt. % of the polyacrylate binder.

In one aspect, the second electrode may further include greater than or equal to about 0.1 wt. % to less than or equal to about 5 wt. % of a conductive additive.

In one aspect, the second electrode may include greater than or equal to about 10 wt. % to less than or equal to about 50 wt. % of the silicon-containing electroactive material.

In one aspect, the second electrode may further include a carbonaceous electroactive material.

In one aspect, the second electrode may include greater than or equal to about 10 wt. % to less than or equal to about 50 wt. % of the silicon-containing electroactive material, and greater than or equal to about 40 wt. % to less than or equal to about 80 wt. % of the carbonaceous electroactive material.

In various aspects, the present disclosure provides a method for forming a silicon-containing electrode. The method may include disposing an electrode forming slurry having a temperature greater than or equal to about 4° C. to less than or equal to about 15° C. one or near a surface of a current collector to form the electrode. The electrode forming slurry may include a silicon-containing electroactive material and a polyacrylate binder.

In one aspect, the method may further include, prior to disposing the electrode forming slurry, holding the electrode forming slurry at the temperature for a holding duration.

In one aspect, the polyacrylate binder may have a molecular weight greater than or equal to about 250,000 g/mol to less than or equal to about 500,000 g/mol and may be formed from monomers selected from the group consisting of:

and combinations thereof.

In one aspect, the electrode forming slurry may further include a conductive additive.

In one aspect, the electrode forming slurry may further include a carbonaceous electroactive material.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific compositions, components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, elements, compositions, steps, integers, operations, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Although the open-ended term “comprising,” is to be understood as a non-restrictive term used to describe and claim various embodiments set forth herein, in certain aspects, the term may alternatively be understood to instead be a more limiting and restrictive term, such as “consisting of” or “consisting essentially of.” Thus, for any given embodiment reciting compositions, materials, components, elements, features, integers, operations, and/or process steps, the present disclosure also specifically includes embodiments consisting of, or consisting essentially of, such recited compositions, materials, components, elements, features, integers, operations, and/or process steps. In the case of “consisting of,” the alternative embodiment excludes any additional compositions, materials, components, elements, features, integers, operations, and/or process steps, while in the case of “consisting essentially of,” any additional compositions, materials, components, elements, features, integers, operations, and/or process steps that materially affect the basic and novel characteristics are excluded from such an embodiment, but any compositions, materials, components, elements, features, integers, operations, and/or process steps that do not materially affect the basic and novel characteristics can be included in the embodiment.

Any method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed, unless otherwise indicated.

When a component, element, or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected, or coupled to the other component, element, or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers and/or sections, these steps, elements, components, regions, layers and/or sections should not be limited by these terms, unless otherwise indicated. These terms may be only used to distinguish one step, element, component, region, layer or section from another step, element, component, region, layer, or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first step, element, component, region, layer, or section discussed below could be termed a second step, element, component, region, layer, or section without departing from the teachings of the example embodiments.

Spatially or temporally relative terms, such as “before,” “after,” “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially or temporally relative terms may be intended to encompass different orientations of the device or system in use or operation in addition to the orientation depicted in the figures.

Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates both exactly or precisely the stated numerical value, and also, that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. For example, “about” may comprise a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.

In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range, including endpoints and sub-ranges given for the ranges.

Example embodiments will now be described more fully with reference to the accompanying drawings.

The present technology relates to electrochemical cells including silicon-containing electrodes and also, to methods of forming and using the same. Such cells can be used in vehicle or automotive transportation applications (e.g., motorcycles, boats, tractors, buses, motorcycles, mobile homes, campers, and tanks). However, the present technology may also be employed in a wide variety of other industries and applications, including aerospace components, consumer goods, devices, buildings (e.g., houses, offices, sheds, and warehouses), office equipment and furniture, and industrial equipment machinery, agricultural or farm equipment, or heavy machinery, by way of non-limiting example. Further, although the illustrated examples detail below include a single positive electrode cathode and a single anode, the skilled artisan will recognize that the present teachings also extend to various other configurations, including those having one or more cathodes and one or more anodes, as well as various current collectors with electroactive layers disposed on or adjacent to one or more surfaces thereof.

An exemplary and schematic illustration of an electrochemical cell (also referred to as a battery)is shown in. The batteryincludes a negative electrode(e.g., anode), a positive electrode(e.g., cathode), and a separatordisposed between the two electrodes,. The separatorprovides electrical separation—prevents physical contact—between the electrodes,. The separatoralso provides a minimal resistance path for internal passage of lithium ions, and in certain instances, related anions, during cycling of the lithium ions. In various aspects, the separatorcomprises an electrolytethat may, in certain aspects, also be present in the negative electrodeand/or the positive electrode, so as to form a continuous electrolyte network. In certain variations, the separatormay be formed by a solid-state electrolyte or a semi-solid-state electrolyte (e.g., gel electrolyte). For example, the separatormay be defined by a plurality of solid-state electrolyte particles. In the instance of solid-state batteries and/or semi-solid-state batteries, the positive electrodeand/or the negative electrodemay include (additionally or alternatively) a plurality of solid-state electrolyte particles. The plurality of solid-state electrolyte particles included in, or defining, the separatormay be the same as or different from the plurality of solid-state electrolyte particles included in the positive electrodeand/or the negative electrode.

A first current collector(e.g., a negative current collector) may be positioned at or near the negative electrode. The first current collectortogether with the negative electrodemay be referred to as a negative electrode assembly. Although not illustrated, the skilled artisan will appreciate that, in certain variations, negative electrodes(also referred to as negative electroactive material layers) may be disposed on one or more parallel sides of the first current collector. Similarly, the skilled artisan will appreciate that, in other variations, a negative electroactive material layer may be disposed on a first side of the first current collector, and a positive electroactive material layer may be disposed on a second side of the first current collector. In each instance, the first current collectormay be a metal foil, metal grid or screen, or expanded metal comprising copper or any other appropriate electrically conductive material known to those of skill in the art.

A second current collector(e.g., a positive current collector) may be positioned at or near the positive electrode. The second current collectortogether with the positive electrodemay be referred to as a positive electrode assembly. Although not illustrated, the skilled artisan will appreciate that, in certain variations, positive electrodes(also referred to as positive electroactive material layers) may be disposed on one or more parallel sides of the second current collector. Similarly, the skilled artisan will appreciate that, in other variations, a positive electroactive material layer may be disposed on a first side of the second current collector, and a negative electroactive material layer may be disposed on a second side of the second current collector. In each instance, the second electrode current collectormay be a metal foil, metal grid or screen, or expanded metal comprising aluminum or any other appropriate electrically conductive material known to those of skill in the art.

The first current collectorand the second current collectormay respectively collect and move free electrons to and from an external circuit. For example, an interruptible external circuitand a load devicemay connect the negative electrode(through the first current collector) and the positive electrode(through the second current collector). The batterycan generate an electric current during discharge by way of reversible electrochemical reactions that occur when the external circuitis closed (to connect the negative electrodeand the positive electrode) and the negative electrodehas a lower potential than the positive electrode. The chemical potential difference between the positive electrodeand the negative electrodedrives electrons produced by a reaction, for example, the oxidation of intercalated lithium, at the negative electrodethrough the external circuittoward the positive electrode. Lithium ions that are also produced at the negative electrodeare concurrently transferred through the electrolytecontained in the separatortoward the positive electrode. The electrons flow through the external circuitand the lithium ions migrate across the separatorcontaining the electrolyteto form intercalated lithium at the positive electrode. As noted above, the electrolyteis typically also present in the negative electrodeand positive electrode. The electric current passing through the external circuitcan be harnessed and directed through the load deviceuntil the lithium in the negative electrodeis depleted and the capacity of the batteryis diminished.

The batterycan be charged or re-energized at any time by connecting an external power source to the lithium ion batteryto reverse the electrochemical reactions that occur during battery discharge. Connecting an external electrical energy source to the batterypromotes a reaction, for example, non-spontaneous oxidation of intercalated lithium, at the positive electrodeso that electrons and lithium ions are produced. The lithium ions flow back toward the negative electrodethrough the electrolyteacross the separatorto replenish the negative electrodewith lithium (e.g., intercalated lithium) for use during the next battery discharge event. As such, a complete discharging event followed by a complete charging event is considered to be a cycle, where lithium ions are cycled between the positive electrodeand the negative electrode. The external power source that may be used to charge the batterymay vary depending on the size, construction, and particular end-use of the battery. Some notable and exemplary external power sources include, but are not limited to, an AC-DC converter connected to an AC electrical power grid though a wall outlet and a motor vehicle alternator.

In many lithium-ion battery configurations, each of the first current collector, negative electrode, separator, positive electrode, and second current collectorare prepared as relatively thin layers (for example, from several microns to a fraction of a millimeter or less in thickness) and assembled in layers connected in electrical parallel arrangement to provide a suitable electrical energy and power package. In various aspects, the batterymay also include a variety of other components that, while not depicted here, are nonetheless known to those of skill in the art. For instance, the batterymay include a casing, gaskets, terminal caps, tabs, battery terminals, and any other conventional components or materials that may be situated within the battery, including between or around the negative electrode, the positive electrode, and/or the separator. The batteryshown inincludes a liquid electrolyteand shows representative concepts of battery operation. However, the present technology also applies to solid-state batteries and/or semi-solid state batteries that include solid-state electrolytes and/or solid-state electrolyte particles and/or semi-solid electrolytes and/or solid-state electroactive particles that may have different designs as known to those of skill in the art.

The size and shape of the batterymay vary depending on the particular application for which it is designed. Battery-powered vehicles and hand-held consumer electronic devices, for example, are two examples where the batterywould most likely be designed to different size, capacity, and power-output specifications. The batterymay also be connected in series or parallel with other similar lithium-ion cells or batteries to produce a greater voltage output, energy, and power if it is required by the load device. Accordingly, the batterycan generate electric current to a load devicethat is part of the external circuit. The load devicemay be powered by the electric current passing through the external circuitwhen the batteryis discharging. While the electrical load devicemay be any number of known electrically-powered devices, a few specific examples include an electric motor for an electrified vehicle, a laptop computer, a tablet computer, a cellular phone, and cordless power tools or appliances. The load devicemay also be an electricity-generating apparatus that charges the batteryfor purposes of storing electrical energy.

With renewed reference to, the positive electrode, the negative electrode, and the separatormay each include an electrolyte solution or systeminside their pores, capable of conducting lithium ions between the negative electrodeand the positive electrode. Any appropriate electrolyte, whether in solid, liquid, or gel form, capable of conducting lithium ions between the negative electrodeand the positive electrodemay be used in the lithium-ion battery. For example, in certain aspects, the electrolytemay be a non-aqueous liquid electrolyte solution (e.g., >1 M) that includes a lithium salt dissolved in an organic solvent or a mixture of organic solvents. Numerous conventional non-aqueous liquid electrolytesolutions may be employed in the battery.

A non-limiting list of lithium salts that may be dissolved in an organic solvent to form the non-aqueous liquid electrolyte solution include lithium hexafluorophosphate (LiPF), lithium perchlorate (LiClO), lithium tetrachloroaluminate (LiAlCl), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF), lithium tetraphenylborate (LiB(CH)), lithium bis (oxalato)borate (LiB(CO)) (LiBOB), lithium difluorooxalatoborate (LiBF(CO)), lithium hexafluoroarsenate (LiAsF), lithium trifluoromethanesulfonate (LiCFSO), lithium bis(trifluoromethane)sulfonylimide (LiN(CFSO)), lithium bis(fluorosulfonyl)imide (LiN(FSO)) (LiSFI), and combinations thereof. These and other similar lithium salts may be dissolved in a variety of non-aqueous aprotic organic solvents, including but not limited to, various alkyl carbonates, such as cyclic carbonates (e.g., ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), and the like), linear carbonates (e.g., dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethylcarbonate (EMC), and the like), aliphatic carboxylic esters (e.g., methyl formate, methyl acetate, methyl propionate, and the like), γ-lactones (e.g., γ-butyrolactone, γ-valerolactone, and the like), chain structure ethers (e.g., 1,2-dimethoxyethane, 1-2-diethoxyethane, ethoxymethoxyethane, and the like), cyclic ethers (e.g., tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, and the like), sulfur compounds (e.g., sulfolane), and combinations thereof.

The separatormay be a porous separator. For example, in certain instances, the separatormay be a microporous polymeric separator including, for example, a polyolefin. The polyolefin may be a homopolymer (derived from a single monomer constituent) or a heteropolymer (derived from more than one monomer constituent), which may be either linear or branched. If a heteropolymer is derived from two monomer constituents, the polyolefin may assume any copolymer chain arrangement, including those of a block copolymer or a random copolymer. Similarly, if the polyolefin is a heteropolymer derived from more than two monomer constituents, it may likewise be a block copolymer or a random copolymer. In certain aspects, the polyolefin may be polyethylene (PE), polypropylene (PP), or a blend of polyethylene (PE) and polypropylene (PP), or multi-layered structured porous films of PE and/or PP. Commercially available polyolefin porous separator membranesinclude CELGARD® 2500 (a monolayer polypropylene separator) and CELGARD® 2320 (a trilayer polypropylene/polyethylene/polypropylene separator) available from Celgard LLC.

When the separatoris a microporous polymeric separator, it may be a single layer or a multi-layer laminate, which may be fabricated from either a dry or a wet process. For example, in certain instances, a single layer of the polyolefin may form the entire separator. In other aspects, the separatormay be a fibrous membrane having an abundance of pores extending between the opposing surfaces and may have an average thickness of less than a millimeter, for example. As another example, however, multiple discrete layers of similar or dissimilar polyolefins may be assembled to form the microporous polymer separator. The separatormay also comprise other polymers in addition to the polyolefin such as, but not limited to, polyethylene terephthalate (PET), polyvinylidene fluoride (PVdF), a polyamide, polyimide, poly(amide-imide) copolymer, polyetherimide, and/or cellulose, or any other material suitable for creating the required porous structure. The polyolefin layer, and any other optional polymer layers, may further be included in the separatoras a fibrous layer to help provide the separatorwith appropriate structural and porosity characteristics.

In certain aspects, the separatormay further include one or more of a ceramic material and a heat-resistant material. For example, the separatormay also be admixed with the ceramic material and/or the heat-resistant material, or one or more surfaces of the separatormay be coated with the ceramic material and/or the heat-resistant material. In certain variations, the ceramic material and/or the heat-resistant material may be disposed on one or more sides of the separator. The ceramic material may be selected from the group consisting of: alumina (AlO), silica (SiO), and combinations thereof. The heat-resistant material may be selected from the group consisting of: Nomex, Aramid, and combinations thereof.